Stereographs (also known by names such as stereograms, stereo views, stereo cards stereoscopic cards, etc.) were a popular hand-held amusement between 1850-1930. Stereographs were made by taking two photographs of the same scene at positions separated by a distance roughly equivalent to the distance between the eyes. The photographs were then pasted side-by-side onto a heavy card measuring roughly 3.5 inches high×7 inches wide. Viewed through a stereoscope, one saw the illusion of a 3D image similar to normal binocular vision. Today, stereographs can be found in the archives of museums and libraries, as well as in antique stores and attics. They are beloved by collectors and are enjoying a comeback in this age of 3D movies and TV. Some contemporary artists also make images in the stereograph format.
The Holmes-type stereoscope, designed by Oliver Wendell Holmes in 1859 and copied by many manufacturers, was the common device for viewing stereographs. Although long-regarded as the best solution for stereograph viewing due to its fine optics, light-blocking lens hood, and easy focusing, the Holmes viewer is seldom available for use in public archives because it is a fragile antique, vulnerable to wear. Sometimes a Holmes viewer is included in an exhibition with a stereograph in its holder, but usually this configuration is inside a display case and not intended for functional use. Most importantly in relation to my invention, the Holmes viewer was designed for hand-held viewing of stereographs and is altogether useless for viewing stereographs that are framed or in exhibition cases. In this form of presentation, oftentimes no viewer is provided, although sometimes inferior viewers are utilized (such as lorgnettes which have poor optics, lack a lens hood and are difficult to use).